Adolescents, particularly female adolescents, are at high risk for sexually acquired HIV and other sexually transmitted diseases (STDs). Adolescents are engaging in sexual intercourse at younger ages, having sex with multiple partners, and inconsistently using condoms. As a result, nearly 3 million sexually active teens become infected with STDs annually, and increasing numbers are being infected with HIV. Adolescent HIV-related sexual risk behaviors have been studied using the same methods and approaches that are used to study adolescent risk behaviors such as alcohol and drug use. As a result, much of what we know about adolescent HIV-related sexual risk behavior is based upon individual-level studies. However, unlike adolescent risk behaviors such as alcohol and drug use, HIV and STD risk results from inter-individual behaviors. Individual sexual behaviors that do not involve others (e.g., masturbation) do not pose any significant risk. Characteristics of the partner and the relationship and influences from the dyad context have been largely overlooked in studies of adolescent sexual risk. This oversight may be particularly significant in limiting our understanding of HIV and STD risk in young women due to the importance women place on relationships, traditional gender role norms, power differences within heterosexual relationships, and a reliance on male partners to use condoms. The purpose of the proposed study is to undertake a dyadic ecological analysis that evaluates the influence of individual, partner, and parental characteristics and dyad-relationship factors on adolescent sexual risk behaviors. The dyadic ecological model for the study draws on Bandura's social cognitive theory, Fishbein and Ajzen's theory of reasoned action, and Bronfenbrenner's ecological model. We propose to perform a secondary analysis of data from the National Longitudinal Study of Adolescent Health (Add Health), wherein we will link data from female adolescents, their parents, their male adolescent partners, and their partners' parents. Measures from adolescents and their parents will be used, in conjunction with characteristics of the teen dyad/relationship, to predict the likelihood of engaging in selected sexual risk behaviors twelve months later (Wave 2). Data will be analyzed using hierarchical logistic regression models. The utility of individual and dyadic ecological models will be compared using goodness-of-fit statistics. Study findings will contribute to our understanding of HIV-related sexual risk among adolescents, and further the development of HIV prevention programs that address the dyad context in which sexual risk occurs.